Attention in prayers (salat) is obligatory for momineen

Verily, the hypocrites seek to deceive Allâh, but it is He Who deceives them.[] And when they stand up for As-Salât (the prayer), they stand with laziness and to be seen of men, and they do not remember Allâh but little.

(They are) swaying between this and that, belonging neither to these nor to those, and he whom Allâh sends astray, you will not find for him a way (to the truth - Islâm).

An-Nisa 143

Comment

After reading this verse ,i am of the view that just performing the elements of Salat (prayer isn't enough) we should have the proper feeling of standing in front of Allah,bowing before him.We should have a feeling that we are no one but humble servants of Allah.

It is not fair for us that while performing Salat (prayer),worldly affairs be running in our minds.If we cant concentrate probably its an indication of our weak faith.
Second that we come to know from this verse is that we should make zikr of Allah as much as we can to make Him pleased with us because it is a sign of hypocrites mentioned in the above verse that they do not make zikr of Allah but little.

Namaz e Khauf

When you (O Messenger Muhammad SAW) are among them, and lead them in As-Salât (the prayer), let one party of them stand up [in Salât (prayer)] with you taking their arms with them; when they finish their prostrations, let them take their positions in the rear and let the other party come up which have not yet prayed, and let them pray with you taking all the precautions and bearing arms. Those who disbelieve wish, if you were negligent of your arms and your baggage, to attack you in a single rush, but there is no sin on you if you put away your arms because of the inconvenience of rain or because you are ill, but take every precaution for yourselves. Verily, Allâh has prepared a humiliating torment for the disbelievers

An-Nisa 102

Namaz e Qasr

And when you (Muslims) travel in the land, there is no sin on you if you shorten As-Salât (the prayer) if you fear that the disbelievers may put you in trial (attack you etc.), verily, the disbelievers are ever unto you open enemies.

An-Nisa 101